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Underwater acoustic observatory installed on the east coast of Antarctica

Camille Lin 28. January 2025 | Antarctica, Science

Against all odds, a team of divers set up hydrophones at a depth of 20 meters to listen to the ocean half a nautical mile from the Dumont-d’Urville station.

In Terre Adélie, the deeper you go, the greater the biodiversity. Image: Amice Erwan / French Polar Institute / CNRS

“Opening an 80-centimeter hole in 1 m 60 of pack ice in the Arctic could take us 8 hours with a saw and hand auger, with four or five people. Here, with two people, we drilled an opening and dived in 20 minutes, using a machine inspired by forestry augers and adapted to ice conditions. The tool was available in Antarctica, so it was a real luxury,” Laurent Chauvaud, CNRS researcher and ice-diving biologist, tells Polar Journal AG on his return from a mission with the French Polar Institute in Brest. “Erwan Amice developed an adapted cylinder prototype with inverted valves, like those used by firefighters. We didn’t have any icing problems.”

Equipped with heated drysuits and modified compressed air cylinders, he worked under the ice in water at -2°C, to install an underwater acoustic observatory not far from the French Dumont-d’Urville polar station. Warned by bad omens, he did not receive Poseidon’s favor, but did manage to position a temporary observatory.

The surface water temperature is negative, but it doesn’t freeze thanks to the salt. Image: Amice Erwan / French Polar Institute / CNRS

“I wasn’t very lucky,” he told us. “We left on November 30… everything was fine until we boarded theAstrolabe in Hobart, after a 25-hour flight.” The French military supply ship to Antarctica found itself blocked by the ice belt orbiting the continent. Five to seven days are usually enough to reach the station, but in this case, “it took us 14 days”, he explains. The ship banged its way through the ice. The atmosphere was truly polar and adventurous, but for Laurent Chauvaud, “it was a bit long. At this stage, we knew that if we lost a week’s work on site, we’d still have to deal with the sea and ice conditions in this part of the world, which are, after all, predictable at this time of year.”

Continuing its journey, a second punishment befell the diving team. Two of his colleagues had to be evacuated for medical and personal reasons. Laurent Chauvaud found himself alone, and French legislation only allowed underwater work in the presence of other professional divers. The biologist then met Gérald Malaussena on the base, who was also a scuba diver. Business picked up.

In this environment, animals move slowly, like this Antarctic sea urchin, Sterechinus neumayeri. Image: Amice Erwan / French Polar Institute / CNRS

“I had anticipated an eventual failure in the deployment of a cabled observatory,” he adds, a little smiling. “That project was postponed for a year, but fortunately, battery-operated autonomous equipment was in our luggage. So we were able to install sensors.” Today, hydrophones record sounds from the sea at depths of between 5 and 16 meters, but scientists have no direct access to the recordings. We’ll have to wait for the next mission.

The divers installed them in an open crater one hundred meters in diameter. “The place looks like a small Roman amphitheater, the rock is half-moon-shaped,” he describes. “At the bottom, the sensors are placed on a small beach.” The researchers chose this location to prevent an iceberg from crushing the installation.

The state of the sea, penguins swimming, seals whistling and the sound of ice… the soundscape is being listened to. Around the hydrophones live starfish, brittle stars, marine worms and sponges. “Some of the sound comes from invertebrates lying on the seabed, like that produced by the stinging of sea urchins,” he explains. “I wasn’t able to deploy the sensors intended for bivalves. The dives were too time-consuming.”

To reach the dive site, all the equipment has to be transported on a ski-doo. Image: Amice Erwan / French Polar Institute / CNRS

The observatory’s installation is still financed for 3 years, the time he has left to improve it and wire it up. “After that, I won’t be managing it; it will be passed on to an institute, like the Institut Universitaire Européen de la Mer, for example, which has a vocation for observing the sciences of the universe and a polar focus”, he explains.

Laurent Chauvaud is on his 20th polar mission, and is currently working mainly on the impact of noise on marine invertebrates. “Even though we have information on the impact of underwater noise on lobsters and scallops, there is no legislation on the noise threshold not to be exceeded in France,” he notes. “It’s only for marine mammals that there are caveats, and to make any, we need scientific data.”

Camille Lin, Polar Journal AG

Is noise pollution around Antarctica regulated?

Underwater landscape around McMurdo Station. Image: Steve Clabuesch/NSF/USAP/PD/USGov

Last September, the Amure laboratory took stock of regulations on underwater noise around Antarctica, from the Lapérouse library, perched on the heights of the Institut Universitaire Européen de la Mer, overlooking the Atlantic.

“Often, there are regulations after an impact, but in this case, it’s not very tangible, because it’s not very perceptible to humans,” explains Adéla Si Saber Berteletti, who holds a master’s degree in international law. She examined several legal frameworks to complete her master’s degree, with the help of Anne Choquet, a teacher-researcher in polar law. “There’s nothing on the subject in international texts on marine pollution, such as MARPOL – which has more in common with oil spills. But, for example, the French Southern and Antarctic Lands [TAAF, editor’s note] regulate the sound emitted by scientists’ acoustic instruments in their waters. This does not directly concern the Southern Ocean.”

The conclusions of Adéla Si Saber Berteletti’s study underline “the importance of strengthening the rules in this area, particularly in the context of the environmental impact assessments required prior to any activity [in Antarctica, editor’s note].” C.L.

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